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diff --git a/gdb/gdb.texinfo b/gdb/gdb.texinfo index db83964..8e98d8b 100644 --- a/gdb/gdb.texinfo +++ b/gdb/gdb.texinfo @@ -1,10 +1,11 @@ \input texinfo -@setfilename ../info/gdb +@setfilename gdb.info @settitle GDB, The GNU Debugger +@synindex ky cp @ifinfo This file documents the GNU debugger GDB. -Copyright (C) 1988 Free Software Foundation, Inc. +Copyright (C) 1988, 1989 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice @@ -19,16 +20,16 @@ notice identical to this one except for the removal of this paragraph @end ignore Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the -sections entitled ``Distribution'' and ``GDB General Public License'' are -included exactly as in the original, and provided that the entire resulting -derived work is distributed under the terms of a permission notice -identical to this one. +section entitled ``GNU General Public License'' is included exactly as +in the original, and provided that the entire resulting derived work is +distributed under the terms of a permission notice identical to this +one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, -except that the sections entitled ``Distribution'' and ``GDB General Public -License'' may be included in a translation approved by the author instead -of in the original English. +except that the section entitled ``GNU General Public License'' may be +included in a translation approved by the author instead of in the +original English. @end ifinfo @setchapternewpage odd @@ -39,9 +40,9 @@ of in the original English. @sp 1 @center The GNU Source-Level Debugger @sp 4 -@center Third Edition, GDB version 3.1 +@center Third Edition, GDB version 3.2 @sp 1 -@center January 1989 +@center April 1989 @sp 5 @center Richard M. Stallman @page @@ -54,20 +55,20 @@ are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the -sections entitled ``Distribution'' and ``GDB General Public License'' are -included exactly as in the original, and provided that the entire resulting -derived work is distributed under the terms of a permission notice -identical to this one. +section entitled ``GNU General Public License'' is included exactly as +in the original, and provided that the entire resulting derived work is +distributed under the terms of a permission notice identical to this +one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, -except that the sections entitled ``Distribution'' and ``GDB General Public -License'' may be included in a translation approved by the author instead -of in the original English. +except that the section entitled ``GNU General Public License'' may be +included in a translation approved by the author instead of in the +original English. @end titlepage @page -@node Top, Commands,, (DIR) +@node Top, Top, Top, (DIR) @unnumbered Summary of GDB The purpose of a debugger such as GDB is to allow you to execute another @@ -97,10 +98,10 @@ is being implemented, and Fortran support will be added when a GNU Fortran compiler is written. @menu -* License:: The GDB General Public License gives you permission +* License:: The GNU General Public License gives you permission to redistribute GDB on certain terms; and also explains that there is no warranty. -* Input:: GDB command syntax and input conventions. +* User Interface:: GDB command syntax and input and output conventions. * Files:: Specifying files for GDB to operate on. * Options:: GDB arguments and options. * Compilation::Compiling your program so you can debug it. @@ -118,95 +119,128 @@ Fortran compiler is written. * Concepts:: Index of GDB concepts. @end menu -@node License, Input, Top, Top -@unnumbered GDB General Public License -@center (Clarified 11 Feb 1988) +@node License, User Interface, Top, Top +@unnumbered GNU GENERAL PUBLIC LICENSE +@center Version 1, February 1989 + +@display +Copyright @copyright{} 1989 Free Software Foundation, Inc. +675 Mass Ave, Cambridge, MA 02139, USA + +Everyone is permitted to copy and distribute verbatim copies +of this license document, but changing it is not allowed. +@end display + +@unnumberedsec Preamble + + The license agreements of most software companies try to keep users +at the mercy of those companies. By contrast, our General Public +License is intended to guarantee your freedom to share and change free +software---to make sure the software is free for all its users. The +General Public License applies to the Free Software Foundation's +software and to any other program whose authors commit to using it. +You can use it for your programs, too. + + When we speak of free software, we are referring to freedom, not +price. Specifically, the General Public License is designed to make +sure that you have the freedom to give away or sell copies of free +software, that you receive source code or can get it if you want it, +that you can change the software or use pieces of it in new free +programs; and that you know you can do these things. + + To protect your rights, we need to make restrictions that forbid +anyone to deny you these rights or to ask you to surrender the rights. +These restrictions translate to certain responsibilities for you if you +distribute copies of the software, or if you modify it. + + For example, if you distribute copies of a such a program, whether +gratis or for a fee, you must give the recipients all the rights that +you have. You must make sure that they, too, receive or can get the +source code. And you must tell them their rights. + + We protect your rights with two steps: (1) copyright the software, and +(2) offer you this license which gives you legal permission to copy, +distribute and/or modify the software. + + Also, for each author's protection and ours, we want to make certain +that everyone understands that there is no warranty for this free +software. If the software is modified by someone else and passed on, we +want its recipients to know that what they have is not the original, so +that any problems introduced by others will not reflect on the original +authors' reputations. + + The precise terms and conditions for copying, distribution and +modification follow. - The license agreements of most software companies keep you at the mercy -of those companies. By contrast, our general public license is intended to -give everyone the right to share GDB. To make sure that you get the rights -we want you to have, we need to make restrictions that forbid anyone to -deny you these rights or to ask you to surrender the rights. Hence this -license agreement. - - Specifically, we want to make sure that you have the right to give away -copies of GDB, that you receive source code or else can get it if you want -it, that you can change GDB or use pieces of it in new free programs, and -that you know you can do these things. - - To make sure that everyone has such rights, we have to forbid you to -deprive anyone else of these rights. For example, if you distribute copies -of GDB, you must give the recipients all the rights that you have. You -must make sure that they, too, receive or can get the source code. And you -must tell them their rights. - - Also, for our own protection, we must make certain that everyone finds -out that there is no warranty for GDB. If GDB is modified by someone else -and passed on, we want its recipients to know that what they have is not -what we distributed, so that any problems introduced by others will not -reflect on our reputation. - - Therefore we (Richard Stallman and the Free Software Foundation, -Inc.) make the following terms which say what you must do to be -allowed to distribute or change GDB. - -@unnumberedsec Copying Policies +@iftex +@unnumberedsec TERMS AND CONDITIONS +@end iftex +@ifinfo +@center TERMS AND CONDITIONS +@end ifinfo @enumerate @item -You may copy and distribute verbatim copies of GDB source code as you -receive it, in any medium, provided that you conspicuously and -appropriately publish on each file a valid copyright notice ``Copyright -@copyright{} 1988 Free Software Foundation, Inc.'' (or with whatever year -is appropriate); keep intact the notices on all files that -refer to this License Agreement and to the absence of any warranty; and -give any other recipients of the GDB program a copy of this License -Agreement along with the program. You may charge a distribution fee -for the physical act of transferring a copy. +This License Agreement applies to any program or other work which +contains a notice placed by the copyright holder saying it may be +distributed under the terms of this General Public License. The +``Program'', below, refers to any such program or work, and a ``work based +on the Program'' means either the Program or any work containing the +Program or a portion of it, either verbatim or with modifications. Each +licensee is addressed as ``you''. + +@item +You may copy and distribute verbatim copies of the Program's source +code as you receive it, in any medium, provided that you conspicuously and +appropriately publish on each copy an appropriate copyright notice and +disclaimer of warranty; keep intact all the notices that refer to this +General Public License and to the absence of any warranty; and give any +other recipients of the Program a copy of this General Public License +along with the Program. You may charge a fee for the physical act of +transferring a copy. @item -You may modify your copy or copies of GDB source code or any portion -of it, and copy and distribute such modifications under the terms of -Paragraph 1 above, provided that you also do the following: +You may modify your copy or copies of the Program or any portion of +it, and copy and distribute such modifications under the terms of Paragraph +1 above, provided that you also do the following: @itemize @bullet @item -cause the modified files to carry prominent notices stating -that you changed the files and the date of any change; and +cause the modified files to carry prominent notices stating that +you changed the files and the date of any change; and @item cause the whole of any work that you distribute or publish, that -in whole or in part contains or is a derivative of GDB or any -part thereof, to be licensed at no charge to all third parties on -terms identical to those contained in this License Agreement -(except that you may choose to grant more extensive warranty -protection to some or all third parties, at your option). +in whole or in part contains the Program or any part thereof, either +with or without modifications, to be licensed at no charge to all +third parties under the terms of this General Public License (except +that you may choose to grant warranty protection to some or all +third parties, at your option). @item -if the modified program serves as a debugger, cause it, when -started running in the simplest and usual way, to print an -announcement including a valid copyright notice ``Copyright -@copyright{} 1988 Free Software Foundation, Inc.'' (or with the -year that is appropriate), saying that there is no warranty (or -else, saying that you provide a warranty) and that users may -redistribute the program under these conditions, and telling the -user how to view a copy of this License Agreement. +If the modified program normally reads commands interactively when +run, you must cause it, when started running for such interactive use +in the simplest and most usual way, to print or display an +announcement including an appropriate copyright notice and a notice +that there is no warranty (or else, saying that you provide a +warranty) and that users may redistribute the program under these +conditions, and telling the user how to view a copy of this General +Public License. @item -You may charge a distribution fee for the physical act of -transferring a copy, and you may at your option offer warranty -protection in exchange for a fee. +You may charge a fee for the physical act of transferring a +copy, and you may at your option offer warranty protection in +exchange for a fee. @end itemize -Mere aggregation of another unrelated program with this program (or its +Mere aggregation of another independent work with the Program (or its derivative) on a volume of a storage or distribution medium does not bring -the other program under the scope of these terms. +the other work under the scope of these terms. @item -You may copy and distribute GDB (or a portion or derivative of it, -under Paragraph 2) in object code or executable form under the terms -of Paragraphs 1 and 2 above provided that you also do one of the -following: +You may copy and distribute the Program (or a portion or derivative of +it, under Paragraph 2) in object code or executable form under the terms of +Paragraphs 1 and 2 above provided that you also do one of the following: @itemize @bullet @item @@ -216,8 +250,8 @@ Paragraphs 1 and 2 above; or, @item accompany it with a written offer, valid for at least three -years, to give any third party free (except for a nominal -shipping charge) a complete machine-readable copy of the +years, to give any third party free (except for a nominal charge +for the cost of distribution) a complete machine-readable copy of the corresponding source code, to be distributed under the terms of Paragraphs 1 and 2 above; or, @@ -228,70 +262,175 @@ allowed only for noncommercial distribution and only if you received the program in object code or executable form alone.) @end itemize -For an executable file, complete source code means all the source code -for all modules it contains; but, as a special exception, it need not -include source code for modules which are standard libraries that -accompany the operating system on which the executable file runs. +Source code for a work means the preferred form of the work for making +modifications to it. For an executable file, complete source code means +all the source code for all modules it contains; but, as a special +exception, it need not include source code for modules which are standard +libraries that accompany the operating system on which the executable +file runs, or for standard header files or definitions files that +accompany that operating system. @item -You may not copy, sublicense, distribute or transfer GDB except as -expressly provided under this License Agreement. Any attempt -otherwise to copy, sublicense, distribute or transfer GDB is void and -your rights to use GDB under this License agreement shall be -automatically terminated. However, parties who have received computer -software programs from you with this License Agreement will not have -their licenses terminated so long as such parties remain in full -compliance. +You may not copy, modify, sublicense, distribute or transfer the +Program except as expressly provided under this General Public License. +Any attempt otherwise to copy, modify, sublicense, distribute or transfer +the Program is void, and will automatically terminate your rights to use +the Program under this License. However, parties who have received +copies, or rights to use copies, from you under this General Public +License will not have their licenses terminated so long as such parties +remain in full compliance. @item -If you wish to incorporate parts of GDB into other free programs whose -distribution conditions are different, write to the Free Software -Foundation. We have not yet worked out a simple rule that can be -stated here, but we will often permit this. We will be guided by the -two goals of preserving the free status of all derivatives our free -software and of promoting the sharing and reuse of software. +By copying, distributing or modifying the Program (or any work based +on the Program) you indicate your acceptance of this license to do so, +and all its terms and conditions. + +@item +Each time you redistribute the Program (or any work based on the +Program), the recipient automatically receives a license from the original +licensor to copy, distribute or modify the Program subject to these +terms and conditions. You may not impose any further restrictions on the +recipients' exercise of the rights granted herein. + +@item +The Free Software Foundation may publish revised and/or new versions +of the General Public License from time to time. Such new versions will +be similar in spirit to the present version, but may differ in detail to +address new problems or concerns. + +Each version is given a distinguishing version number. If the Program +specifies a version number of the license which applies to it and ``any +later version'', you have the option of following the terms and conditions +either of that version or of any later version published by the Free +Software Foundation. If the Program does not specify a version number of +the license, you may choose any version ever published by the Free Software +Foundation. + +@item +If you wish to incorporate parts of the Program into other free +programs whose distribution conditions are different, write to the author +to ask for permission. For software which is copyrighted by the Free +Software Foundation, write to the Free Software Foundation; we sometimes +make exceptions for this. Our decision will be guided by the two goals +of preserving the free status of all derivatives of our free software and +of promoting the sharing and reuse of software generally. + +@iftex +@heading NO WARRANTY +@end iftex +@ifinfo +@center NO WARRANTY +@end ifinfo + +@item +BECAUSE THE PROGRAM IS LICENSED FREE OF CHARGE, THERE IS NO WARRANTY +FOR THE PROGRAM, TO THE EXTENT PERMITTED BY APPLICABLE LAW. EXCEPT WHEN +OTHERWISE STATED IN WRITING THE COPYRIGHT HOLDERS AND/OR OTHER PARTIES +PROVIDE THE PROGRAM ``AS IS'' WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED +OR IMPLIED, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF +MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS +TO THE QUALITY AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE +PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY SERVICING, +REPAIR OR CORRECTION. + +@item +IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING WILL +ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MAY MODIFY AND/OR +REDISTRIBUTE THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, +INCLUDING ANY GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES +ARISING OUT OF THE USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT +LIMITED TO LOSS OF DATA OR DATA BEING RENDERED INACCURATE OR LOSSES +SUSTAINED BY YOU OR THIRD PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE +WITH ANY OTHER PROGRAMS), EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN +ADVISED OF THE POSSIBILITY OF SUCH DAMAGES. @end enumerate @iftex -@vfil -@eject +@heading END OF TERMS AND CONDITIONS @end iftex -@unnumberedsec NO WARRANTY - - BECAUSE GDB IS LICENSED FREE OF CHARGE, WE PROVIDE ABSOLUTELY -NO WARRANTY, TO THE EXTENT PERMITTED BY APPLICABLE STATE LAW. EXCEPT -WHEN OTHERWISE STATED IN WRITING, THE FREE SOFTWARE FOUNDATION, INC, -RICHARD M. STALLMAN AND/OR OTHER PARTIES PROVIDE GDB ``AS IS'' -WITHOUT WARRANTY OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, -BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND -FITNESS FOR A PARTICULAR PURPOSE. THE ENTIRE RISK AS TO THE QUALITY -AND PERFORMANCE OF THE PROGRAM IS WITH YOU. SHOULD THE GDB -PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF ALL NECESSARY -SERVICING, REPAIR OR CORRECTION. - - IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW WILL FREE SOFTWARE -FOUNDATION, INC., RICHARD M. STALLMAN, AND/OR ANY OTHER PARTY WHO MAY -MODIFY AND REDISTRIBUTE GDB AS PERMITTED ABOVE, BE LIABLE TO YOU -FOR DAMAGES, INCLUDING ANY LOST PROFITS, LOST MONIES, OR OTHER -SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE USE OR -INABILITY TO USE (INCLUDING BUT NOT LIMITED TO LOSS OF DATA OR DATA -BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY THIRD PARTIES OR A -FAILURE OF THE PROGRAM TO OPERATE WITH PROGRAMS NOT DISTRIBUTED BY -FREE SOFTWARE FOUNDATION, INC.) THE PROGRAM, EVEN IF YOU HAVE BEEN -ADVISED OF THE POSSIBILITY OF SUCH DAMAGES, OR FOR ANY CLAIM BY ANY -OTHER PARTY. - -@node Input, Files, License, Top -@chapter GDB Input Conventions +@ifinfo +@center END OF TERMS AND CONDITIONS +@end ifinfo + +@page +@unnumberedsec Appendix: How to Apply These Terms to Your New Programs + + If you develop a new program, and you want it to be of the greatest +possible use to humanity, the best way to achieve this is to make it +free software which everyone can redistribute and change under these +terms. + + To do so, attach the following notices to the program. It is safest to +attach them to the start of each source file to most effectively convey +the exclusion of warranty; and each file should have at least the +``copyright'' line and a pointer to where the full notice is found. + +@smallexample +@var{one line to give the program's name and a brief idea of what it does.} +Copyright (C) 19@var{yy} @var{name of author} + +This program is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 1, or (at your option) +any later version. + +This program is distributed in the hope that it will be useful, +but WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the +GNU General Public License for more details. + +You should have received a copy of the GNU General Public License +along with this program; if not, write to the Free Software +Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA. +@end smallexample + +Also add information on how to contact you by electronic and paper mail. + +If the program is interactive, make it output a short notice like this +when it starts in an interactive mode: + +@smallexample +Gnomovision version 69, Copyright (C) 19@var{yy} @var{name of author} +Gnomovision comes with ABSOLUTELY NO WARRANTY; for details type `show w'. +This is free software, and you are welcome to redistribute it +under certain conditions; type `show c' for details. +@end smallexample + +The hypothetical commands `show w' and `show c' should show the +appropriate parts of the General Public License. Of course, the +commands you use may be called something other than `show w' and `show +c'; they could even be mouse-clicks or menu items---whatever suits your +program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a ``copyright disclaimer'' for the program, if +necessary. Here a sample; alter the names: + +@example +Yoyodyne, Inc., hereby disclaims all copyright interest in the +program `Gnomovision' (a program to direct compilers to make passes +at assemblers) written by James Hacker. + +@var{signature of Ty Coon}, 1 April 1989 +Ty Coon, President of Vice +@end example + +That's all there is to it! + +@node User Interface, Files, License, Top +@chapter GDB Input and Output Conventions GDB is invoked with the shell command @samp{gdb}. Once started, it reads commands from the terminal until you tell it to exit. A GDB command is a single line of input. There is no limit on how long it can be. It starts with a command name, which is followed by arguments -whose meaning depends on the command name. Some command names do not -allow arguments. +whose meaning depends on the command name. For example, the command +@samp{step} accepts an argument which is the number of times to step, +as in @samp{step 5}. You can also use the @samp{step} command with +no arguments. Some command names do not allow any arguments. +@cindex abbreviation GDB command names may always be abbreviated if the abbreviation is unambiguous. Sometimes even ambiguous abbreviations are allowed; for example, @samp{s} is specially defined as equivalent to @samp{step} @@ -299,6 +438,7 @@ even though there are other commands whose names start with @samp{s}. Possible command abbreviations are often stated in the documentation of the individual commands. +@cindex repeating commands A blank line as input to GDB means to repeat the previous command verbatim. Certain commands do not allow themselves to be repeated this way; these are commands for which unintentional repetition might cause trouble and which @@ -308,25 +448,12 @@ you are unlikely to want to repeat. Certain others (@samp{list} and A line of input starting with @samp{#} is a comment; it does nothing. This is useful mainly in command files (@xref{Command Files}). -Occasionally it is useful to execute a shell command from within gdb. -This can be done with the @samp{shell} command, or the shell escape -character @samp{!}. - -@table @code -@item shell @var{shell command string} -@kindex shell -@item !@var{shell command string} -@kindex ! -@cindex shell escape -Directs GDB to invoke an inferior shell to execute @samp{shell command string}. -The environmental variable @samp{SHELL} is used if it exists, otherwise gdb -uses @samp{/bin/sh}. -@end table - -GDB @dfn{prompts} for commands with a string that is normally @samp{(gdb)}. -When debugging GDB with GDB, it is useful to change the prompt in one of -the GDBs so that you can distinguish them. This can be done with the -@samp{set prompt} command. +@cindex prompt +GDB indicates its readiness to read a command by printing a string +called the @dfn{prompt}. This string is normally @samp{(gdb)}. You can +change the prompt string with the @samp{set prompt} command. For +instance, when debugging GDB with GDB, it is useful to change the prompt +in one of the GDBs so that you tell which one you are talking to. @table @code @item set prompt @var{newprompt} @@ -342,15 +469,62 @@ of any GDB command that is in progress and return to GDB command level. It is safe to type @kbd{Ctrl-c} at any time because GDB does not allow it to take effect until a time when it is safe. -@node Files, Options, Input, Top +@cindex screen size +@cindex pauses in output +Certain commands to GDB may produce large amounts of information output +to the screen. To help you read all of it, GDB pauses and asks you for +input at the end of each page of output. Type @key{RET} when you want +to continue the output. Normally GDB knows the size of the screen from +on the termcap data base together with the value of the @code{TERM} +environment variable; if this is not correct, you can override it with +the @samp{set screensize} command: + +@table @code +@item set screensize @var{lpp} +@itemx set screensize @var{lpp} @var{cpl} +@kindex set screensize +Specify a screen height of @var{lpp} lines and (optionally) a width of +@var{cpl} characters. If you omit @var{cpl}, the width does not change. + +If you specify a height of zero lines, GDB will not pause during output +no matter how long the output is. This is useful if output is to a file +or to an editor buffer. +@end table + +Also, GDB may at times produce more information about its own workings +than is of interest to the user. Some of these informational messages +can be turned on and off with the @samp{set verbose} command: + +@table @code +@kindex set verbose +@item set verbose off +Disables GDB's output of certain informational messages. + +@item set verbose on +Re-enables GDB's output of certain informational messages. +@end table + +Currently, the messages controlled by @samp{set verbose} are those which +announce that the symbol table for a source file is being read +(@pxref{File Commands}, in the description of the command +@samp{symbol-file}). +@c The following is the right way to do it, but emacs 18.55 doesn't support +@c @ref, and neither the emacs lisp manual version of texinfmt or makeinfo +@c is released. +@ignore +see @samp{symbol-file} in @ref{File Commands}). +@end ignore + +@node Files, Compilation, User Interface, Top @chapter Specifying GDB's Files @cindex core dump file @cindex executable file @cindex symbol table -GDB needs to know the filename of the program to be debugged. To debug a -core dump of a previous run, GDB must be told the filename of the core -dump. +GDB needs to know the file name of the program to be debugged, both in +order to read its symbol table and in order to start the program. To +debug a core dump of a previous run, GDB must be told the file name of +the core dump. @menu * Arguments: File Arguments. Specifying files with arguments @@ -375,8 +549,8 @@ specifies @file{progm} as the executable program and @file{core} as a core dump file to examine. (You do not need to have a core dump file if what you plan to do is debug the program interactively.) -@xref{Options}, for full information on command options and arguments for -GDB. +@xref{Options}, for full information on options and arguments for +invoking GDB. @node File Commands,, File Arguments, Files @section Specifying Files with Commands @@ -392,18 +566,38 @@ files are useful. @kindex exec-file Specify that the program to be run is found in @var{filename}. If you do not specify a directory and the file is not found in GDB's working -directory, GDB will use the environment variable @samp{PATH} as a list +directory, GDB will use the environment variable @code{PATH} as a list of directories to search, just as the shell does when looking for a program to run. @item symbol-file @var{filename} @kindex symbol-file -Read symbol table information from file @var{filename}. @samp{PATH} +Read symbol table information from file @var{filename}. @code{PATH} is searched when necessary. Most of the time you will use both the @samp{exec-file} and @samp{symbol-file} commands on the same file. @samp{symbol-file} with no argument clears out GDB's symbol table. +The @samp{symbol-file} command does not actually read the symbol table in +full right away. Instead, it scans the symbol table quickly to find +which source files and which symbols are present. The details are read +later, one source file at a time, when they are needed. + +The purpose of this two-stage reading strategy is to make GDB start up +faster. For the most part, it is invisible except for occasional +messages telling you that the symbol table details for a particular +source file are being read. (The @samp{set verbose} command controls +whether these messages are printed; @pxref{User Interface}). + +However, you will sometimes see in backtraces lines for functions in +source files whose data has not been read in; these lines omit some of +the information, such as argument values, which cannot be printed +without full details of the symbol table. + +When the symbol table is stored in COFF format, @samp{symbol-file} does +read the symbol table data in full right away. We haven't bothered to +implement the two-stage strategy for COFF. + @item core-file @var{filename} @kindex core-file Specify the whereabouts of a core dump file to be used as the @@ -414,29 +608,27 @@ executable file. @samp{core-file} with no argument specifies that no core file is to be used. +Note that the core file is ignored when your program is actually running +under GDB. So, if you have been running the program and you wish to +debug a core file instead, you must kill the subprocess in which the +program is running. To do this, use the @samp{kill} command +(@pxref{Kill Process}). + @item add-file @var{filename} @var{address} @kindex add-file -The @samp{add-file} command takes two arguments, a file name, and the -address at which that file has been (or should be) dynamically loaded. -GDB will then treat that file as though it had always been dynamically -linked, and provide the user with all the normal GDB features, including -symbolic debugging. - -With the @samp{add-file} command, it is possible to debug code which was -not present in the initial load image of the program under test. -Suppose you have a program which can, while running, dynamically link a -program fragment into its address space. One program which does this is -KCL, a free common lisp implementation. The fragment will be loaded -into the main program's address space at some address, and the main -program can then call functions within the fragment by calculating (or -otherwise obtaining) their addresses. - -@item kill -@kindex kill -Cancel running the program under GDB. This could be used if you wish -to debug a core dump instead. GDB ignores any core dump file if it is -actually running the program, so the @samp{kill} command is the only -sure way to go back to using the core dump file. +@cindex dynamic linking +The @samp{add-file} command reads additional symbol table information +from the file @var{filename}. You would use this when that file has +been dynamically loaded into the program that is running. @var{address} +should be the memory address at which the file has been loaded; GDB cannot +figure this out for itself. + +The symbol table of the file @var{filename} is added to the symbol table +originally read with the @samp{symbol-file} command. You can use the +@samp{add-file} command any number of times; the new symbol data thus +read keeps adding to the old. The @samp{symbol-file} command forgets +all the symbol data GDB has read; that is the only time symbol data is +forgotten in GDB. @item info files @kindex info files @@ -454,88 +646,7 @@ auto-display expressions. This is because they may contain pointers to the internal data recording symbols and data types, which are part of the old symbol table data being discarded inside GDB. -@node Options, Compilation, Files, Top -@chapter Options and Arguments for GDB - -When you invoke GDB, you can pass commands telling it what files to -operate on and what other things to do. - -@menu -* Mode Options:: Options controlling modes of operation. -* File Options:: Options to specify files (executable, coredump, commands) -* Other Arguments:: Any other arguments without options - also specify files. -@end menu - -@node Mode Options, File Options, Options, Options -@section Mode Options - -@table @samp -@item -nx -Do not execute commands from the init files @file{.gdbinit}. -Normally, the commands in these files are executed after all the -command options and arguments have been processed. @xref{Command -Files}. - -@item -q -``Quiet''. Do not print the usual introductory messages. - -@item -batch -Run in batch mode. Exit with code 1 after processing all the command -files specified with @samp{-x} (and @file{.gdbinit}, if not -inhibited). Exit also if, due to an error, GDB would otherwise -attempt to read a command from the terminal. - -@item -fullname -This option is used when Emacs runs GDB as a subprocess. It tells GDB -to output the full file name and line number in a standard, -recognizable fashion each time a stack frame is displayed (which -includes each time the program stops). This recognizable format looks -like two @samp{\032} characters, followed by the filename, line number -and character position separated by colons, and a newline. The -Emacs-to-GDB interface program uses the two @samp{\032} characters as -a signal to display the source code for the frame. -@end table - -@node File Options, Other Arguments, Mode Options, Options -@section File-specifying Options - -All the options and command line arguments given are processed -in sequential order. The order makes a difference when the -@samp{-x} command is used. - -@table @samp -@item -s @var{file} -Read symbol table from file @var{file}. - -@item -e @var{file} -Use file @var{file} as the executable file to execute when -appropriate, and for examining pure data in conjunction with a core -dump. - -@item -se @var{file} -Read symbol table from file @var{file} and use it as the executable -file. - -@item -c @var{file} -Use file @var{file} as a core dump to examine. - -@item -x @var{file} -Execute GDB commands from file @var{file}. - -@item -d @var{directory} -Add @var{directory} to the path to search for source files. -@end table - -@node Other Arguments,, File Options, Options -@section Other Arguments - -If there are arguments to GDB that are not options or associated with -options, the first one specifies the symbol table and executable file name -(as if it were preceded by @samp{-se}) and the second one specifies a core -dump file name (as if it were preceded by @samp{-c}). - -@node Compilation, Running, Options, Top +@node Compilation, Running, Files, Top @chapter Compiling Your Program for Debugging In order to debug a program effectively, you need to ask for debugging @@ -555,27 +666,20 @@ possible to debug optimized code. We recommend that you @emph{always} use @samp{-g} whenever you compile a program. You may think the program is correct, but there's no sense in pushing your luck. -If you are using the GNU C compiler, the GNU assembler and the GNU linker, -you can choose between two formats of debugging information: the standard -Unix format, which is what you get with @samp{-g}, and GDB's own format, -which you request by using @samp{-gg} instead of @samp{-g}. This stores -debugging information in the executable file in a format much like that -which is used inside GDB. This has these advantages and disadvantages: +GDB no longer supports the debugging information produced by giving the +GNU C compiler the @samp{-gg} option, so do not use this option. -@itemize @bullet -@item -GDB can read @samp{-gg} format more than twice as fast as Unix -@samp{-g} format. +If your program includes archives made with the @code{ar} program, and +if the object files used as input to @code{ar} were compiled without the +@samp{-g} option and have names longer than 15 characters, GDB will get +confused reading the program's symbol table. No error message will be +given, but GDB may behave strangely. The reason for this problem is a +deficiency in the Unix archive file format, which cannot represent file +names longer than 15 characters. -@item -The @samp{-gg} format uses much more disk space than Unix format. - -@item -The Unix debuggers can understand only Unix format, so you cannot use -Unix source-level debuggers if you compile with @samp{-gg}. (The -@code{adb} debugger works with either format; it does not use this -information in any case.) -@end itemize +To avoid this problem, compile the archive members with the @samp{-g} +option or use shorter file names. Alternatively, use a version of GNU +@code{ar} dated more recently than August 1989. @node Running, Stopping, Compilation, Top @chapter Running Your Program Under GDB @@ -587,16 +691,17 @@ must already have been specified using the @samp{exec-file} command or with an argument to GDB (@pxref{Files}); what @samp{run} does is create an inferior process, load the program into it, and set it in motion. -The execution of a program is affected by certain information it receives -from its superior. GDB provides ways to specify them, which you must do -@i{before} starting the program. (You can change them after starting the -program, but such changes do not affect the program unless you start it -over again.) +The execution of a program is affected by certain information it +receives from its superior. GDB provides ways to specify this +information, which you must do @i{before} starting the program. (You +can change it after starting the program, but such changes do not affect +the program unless you start it over again.) This information may be +divided into three categories: @table @asis @item The @i{arguments.} You specify the arguments to give the program as the arguments of the -@samp{run} command. +@samp{run} command. @item The @i{environment.} The program normally inherits its environment from GDB, but you can @@ -615,7 +720,7 @@ program to stop. @xref{Stopping}. Note that once your program has been started by the @samp{run} command, you may evaluate expressions that involve calls to functions in the inferior. @xref{Expressions}. If you wish to evaluate a function -simply for it's side affects, you may use the @samp{set} command. +simply for its side affects, you may use the @samp{set} command. @xref{Assignment}. @menu @@ -625,13 +730,14 @@ simply for it's side affects, you may use the @samp{set} command. to your program when it is run. * Input/Output:: Specifying the program's standard input and output. * Attach:: Debugging a process started outside GDB. +* Kill Process:: Getting rid of the child process running your program. @end menu @node Arguments, Environment, Running, Running @section Your Program's Arguments @cindex arguments (to your program) -You specify the arguments to give the program as the arguments of the +The arguments to your program are specified by the arguments of the @samp{run} command. They are passed to a shell, which expands wildcard characters and performs redirection of I/O, and thence to the program. @@ -670,7 +776,7 @@ your program when it is started. This command can be abbreviated @samp{i env}. @item set environment @var{varname} @var{value} -@item set environment @var{varname} = @var{value} +@itemx set environment @var{varname} = @var{value} @kindex set environment Sets environment variable @var{varname} to @var{value}, for your program only, not for GDB itself. @var{value} may be any string; the values of @@ -679,25 +785,36 @@ supplied by your program itself. The @var{value} parameter is optional; if it is eliminated, the variable is set to a null value. This command can be abbreviated as short as @samp{set e}. +For example, this command: + +@example +set env USER = foo +@end example + +@noindent +tells the program, when subsequently run, to assume it is being run +on behalf of the user named @samp{foo}. + @item delete environment @var{varname} +@itemx unset environment @var{varname} @kindex delete environment -@item unset environment @var{varname} @kindex unset environment -Remove variable @var{varname} from the environment to be passed to -your program. This is different from @samp{set env @var{varname} =} -because @samp{delete environment} makes a variable not be defined at -all, which is distinguishable from an empty value. This command can -be abbreviated @samp{d e}. +Remove variable @var{varname} from the environment to be passed to your +program. This is different from @samp{set env @var{varname}@ =} because +@samp{delete environment} leaves the variable with no value, which is +distinguishable from an empty value. This command can be abbreviated +@samp{d e}. @end table @node Working Directory, Input/Output, Environment, Running @section Your Program's Working Directory @cindex working directory (of your program) -Each time you start your program with @samp{run}, it inherits its working -directory from the current working directory of GDB. GDB's working -directory is initially whatever it inherited from its superior, but you can -specify the working directory for GDB with the @samp{cd} command. +Each time you start your program with @samp{run}, it inherits its +working directory from the current working directory of GDB. GDB's +working directory is initially whatever it inherited from its parent +process (typically the shell), but you can specify a new working +directory in GDB with the @samp{cd} command. The GDB working directory also serves as a default for the commands that specify files for GDB to operate on. @xref{Files}. @@ -731,49 +848,52 @@ run > outfile starts the program, diverting its output to the file @file{outfile}. @kindex tty -Another way to specify where the program should do input and output is with -the @samp{tty} command. This command accepts a file name as argument, and -causes this file to be the default for future @samp{run} commands. It also -resets the controlling terminal for future @samp{run} commands. For -example, +Another way to specify where the program should do input and output is +with the @samp{tty} command. This command accepts a file name as +argument, and causes this file to be the default for future @samp{run} +commands. It also resets the controlling terminal for the child +process, for future @samp{run} commands. For example, @example tty /dev/ttyb @end example @noindent -directs that processes started with subsequent @samp{run} commands default -to do input and output on the terminal @file{/dev/ttyb} and sets the -controlling terminal to @file{/dev/ttyb}. An explicit redirection in -@samp{run} overrides the @samp{tty} command's effect on input/output -redirection. +directs that processes started with subsequent @samp{run} commands +default to do input and output on the terminal @file{/dev/ttyb} and have +that as their controlling terminal. + +An explicit redirection in @samp{run} overrides the @samp{tty} command's +effect on input/output redirection, but not its effect on the +controlling terminal. When you use the @samp{tty} command or redirect input in the @samp{run} -command, the @emph{input for your program} comes from the specified file, -but the input for GDB still comes from your terminal. +command, only the @emph{input for your program} is affected. The input +for GDB still comes from your terminal. -@node Attach,, Input/Output, Running +@node Attach, Kill Process, Input/Output, Running @section Debugging an Already-Running Process @kindex detach @kindex attach @cindex attach -Some operating systems (in particular, Sun) allow GDB to begin debugging an -already-running process that was started outside of GDB. To do this you -must use the @samp{attach} command instead of the @samp{run} command. +Some operating systems allow GDB to debug an already-running process +that was started outside of GDB. To do this, you use the @samp{attach} +command instead of the @samp{run} command. -The @samp{attach} command requires one argument, which is the process-id of -the process you want to debug. (The usual way to find out the process-id -of the process is with the @samp{ps} utility.) +The @samp{attach} command requires one argument, which is the process-id +of the process you want to debug. (The usual way to find out the +process-id of the process is with the @code{ps} utility.) The first thing GDB does after arranging to debug the process is to stop it. You can examine and modify an attached process with all the GDB commands that ordinarily available when you start processes with @samp{run}. You can insert breakpoints; you can step and continue; you can modify storage. If you would rather the process continue running, -use the @samp{continue} command after attaching. +you may use the @samp{continue} command after attaching GDB to the +process. -When you are finished debugging the attached process, you can use the +When you have finished debugging the attached process, you can use the @samp{detach} command to release it from GDB's control. Detaching the process continues its execution. After the @samp{detach} command, that process and GDB become completely independent once more, and you @@ -783,12 +903,41 @@ If you exit GDB or use the @samp{run} command while you have an attached process, you kill that process. You will be asked for confirmation if you try to do either of these things. +The @samp{attach} command is also used to debug a remote machine via a +serial connection. @xref{Attach}, for more info. + +@node Kill Process,, Attach, Running +@section Killing the Child Process + +@table @code +@item kill +@kindex kill +Kill the child process in which the program being debugged is running +under GDB. + +This command is useful if you wish to debug a core dump instead. GDB +ignores any core dump file if it is actually running the program, so the +@samp{kill} command is the only sure way to make sure the core dump file +is used once again. + +It is also useful if you wish to run the program outside the debugger +for once and then go back to debugging it. + +The @samp{kill} command is also useful if you wish to recompile and +relink the program, since on many systems it is impossible to modify an +executable file which is running in a process. But, in this case, it is +just as good to exit GDB, since you will need to read a new symbol table +after the program is recompiled if you wish to debug the new version, +and restarting GDB is the easiest way to do that. +@end table + @node Stopping, Stack, Running, Top @chapter Stopping and Continuing -When you run a program normally, it runs until exiting. The purpose -of using a debugger is so that you can stop it before that point; -or so that if the program runs into trouble you can find out why. +When you run a program normally, it runs until it terminates. The +principal purpose of using a debugger is so that you can stop it before +that point; or so that if the program runs into trouble you can +investigate and find out why. @menu * Signals:: Fatal signals in your program just stop it; @@ -802,6 +951,7 @@ or so that if the program runs into trouble you can find out why. @node Signals, Breakpoints, Stopping, Stopping @section Signals +@cindex signals A signal is an asynchronous event that can happen in a program. The operating system defines the possible kinds of signals, and gives each kind @@ -811,6 +961,7 @@ gets from referencing a place in memory far away from all the areas in use; @code{SIGALRM} occurs when the alarm clock timer goes off (which happens only if the program has requested an alarm). +@cindex fatal signals Some signals, including @code{SIGALRM}, are a normal part of the functioning of the program. Others, such as @code{SIGSEGV}, indicate errors; these signals are @dfn{fatal} (kill the program immediately) if the @@ -822,6 +973,7 @@ GDB has the ability to detect any occurrence of a signal in the program running under GDB's control. You can tell GDB in advance what to do for each kind of signal. +@cindex handling signals Normally, GDB is set up to ignore non-erroneous signals like @code{SIGALRM} (so as not to interfere with their role in the functioning of the program) but to stop the program immediately whenever an error signal happens. @@ -904,23 +1056,23 @@ enable it again. @kindex info break @kindex $_ The command @samp{info break} prints a list of all breakpoints set and not -cleared, showing their numbers, where in the program they are, and any +deleted, showing their numbers, where in the program they are, and any special features in use for them. Disabled breakpoints are included in the list, but marked as disabled. @samp{info break} with a breakpoint number -as argument lists only that breakpoint. The convenience variable @samp{$_} +as argument lists only that breakpoint. The convenience variable @code{$_} and the default examining-address for the @samp{x} command are set to the address of the last breakpoint listed (@pxref{Memory}). @menu * Set Breaks:: How to establish breakpoints. -* Clear Breaks:: How to remove breakpoints no longer needed. +* Delete Breaks:: How to remove breakpoints no longer needed. * Disabling:: How to disable breakpoints (turn them off temporarily). * Conditions:: Making extra conditions on whether to stop. * Break Commands:: Commands to be executed at a breakpoint. * Error in Breakpoints:: "Cannot insert breakpoints" error--why, what to do. @end menu -@node Set Breaks, Clear Breaks, Breakpoints, Breakpoints +@node Set Breaks, Delete Breaks, Breakpoints, Breakpoints @subsection Setting Breakpoints @kindex break @@ -931,6 +1083,11 @@ You have several ways to say where the breakpoint should go. @item break @var{function} Set a breakpoint at entry to function @var{function}. +@item break @var{+offset} +@itemx break @var{-offset} +Set a breakpoint some number of lines forward or back from the position +at which execution stopped in the currently selected frame. + @item break @var{linenum} Set a breakpoint at line @var{linenum} in the current source file. That file is the last file whose source text was printed. This @@ -942,7 +1099,7 @@ Set a breakpoint at line @var{linenum} in source file @var{filename}. @item break @var{filename}:@var{function} Set a breakpoint at entry to function @var{function} found in file -@var{filename}. Specifying a filename as well as a function name is +@var{filename}. Specifying a file name as well as a function name is superfluous except when multiple files contain similarly named functions. @@ -956,11 +1113,15 @@ Set a breakpoint at the next instruction to be executed in the selected stack frame (@pxref{Stack}). In any selected frame but the innermost, this will cause the program to stop as soon as control returns to that frame. This is equivalent to a @samp{finish} command in the frame -inside the selected frame. If this is done in the innermost frame gdb +inside the selected frame. If this is done in the innermost frame, GDB will stop the next time it reaches the current location; this may be -useful inside of loops. It does not stop at this breakpoint immediately -upon continuation of the program since no code would be executed if it -did. +useful inside of loops. + +GDB normally ignores breakpoints when it resumes execution, until at +least one instruction has been executed. If it did not do this, you +would be unable to proceed past a breakpoint without first disabling the +breakpoint. This rule applies whether or not the breakpoint already +existed when the program stopped. @item break @dots{} if @var{cond} Set a breakpoint with condition @var{cond}; evaluate the expression @@ -973,61 +1134,60 @@ arguments described above (or no argument) specifying where to break. @kindex tbreak Set a breakpoint enabled only for one stop. @var{args} are the same as in the @samp{break} command, and the breakpoint is set in the same -way, but the breakpoint is automatically @dfn{disabled} the first time it -is hit. +way, but the breakpoint is automatically disabled the first time it +is hit. @xref{Disabling}. @end table GDB allows you to set any number of breakpoints at the same place in the program. There is nothing silly or meaningless about this. When the breakpoints are conditional, this is even useful (@pxref{Conditions}). -@node Clear Breaks, Disabling, Set Breaks, Breakpoints -@subsection Clearing Breakpoints +@node Delete Breaks, Disabling, Set Breaks, Breakpoints +@subsection Deleting Breakpoints -@cindex clear breakpoint -@cindex delete breakpoints +@cindex clearing breakpoint +@cindex deleting breakpoints It is often necessary to eliminate a breakpoint once it has done its job and you no longer want the program to stop there. This is called -@dfn{clearing} or @samp{deleting} the breakpoint. A breakpoint that -has been cleared no longer exists in any sense. +@dfn{deleting} the breakpoint. A breakpoint that has been deleted no +longer exists in any sense; it is forgotten. -With the @samp{clear} command you can clear breakpoints according to where -they are in the program. With the @samp{delete} command you can clear +With the @samp{clear} command you can delete breakpoints according to where +they are in the program. With the @samp{delete} command you can delete individual breakpoints by specifying their breakpoint numbers. -@b{It is not necessary to clear a breakpoint to proceed past it.} GDB +@b{It is not necessary to delete a breakpoint to proceed past it.} GDB automatically ignores breakpoints in the first instruction to be executed -when you continue execution at the same address where the program stopped. +when you continue execution without changing the execution address. @table @code @item clear @kindex clear -Clear any breakpoints at the next instruction to be executed in the +Delete any breakpoints at the next instruction to be executed in the selected stack frame (@pxref{Selection}). When the innermost frame -is selected, this is a good way to clear a breakpoint that the program +is selected, this is a good way to delete a breakpoint that the program just stopped at. @item clear @var{function} @itemx clear @var{filename}:@var{function} -Clear any breakpoints set at entry to the function @var{function}. +Delete any breakpoints set at entry to the function @var{function}. @item clear @var{linenum} -@item clear @var{filename}:@var{linenum} -Clear any breakpoints set at or within the code of the specified line. +@itemx clear @var{filename}:@var{linenum} +Delete any breakpoints set at or within the code of the specified line. @item delete @var{bnums}@dots{} @kindex delete Delete the breakpoints of the numbers specified as arguments. -A breakpoint deleted is forgotten completely. @end table -@node Disabling, Conditions, Clear Breaks, Breakpoints +@node Disabling, Conditions, Delete Breaks, Breakpoints @subsection Disabling Breakpoints @cindex disabled breakpoints @cindex enabled breakpoints -Rather than clearing a breakpoint, you might prefer to @dfn{disable} it. -This makes the breakpoint inoperative as if it had been cleared, but +Rather than deleting a breakpoint, you might prefer to @dfn{disable} it. +This makes the breakpoint inoperative as if it had been deleted, but remembers the information on the breakpoint so that you can @dfn{enable} it again later. @@ -1058,8 +1218,8 @@ commands: @table @code @item disable breakpoints @var{bnums}@dots{} +@itemx disable @var{bnums}@dots{} @kindex disable breakpoints -@item disable @var{bnums}@dots{} @kindex disable Disable the specified breakpoints. A disabled breakpoint has no effect but is not forgotten. All options such as ignore-counts, @@ -1067,20 +1227,20 @@ conditions and commands are remembered in case the breakpoint is enabled again later. @item enable breakpoints @var{bnums}@dots{} +@itemx enable @var{bnums}@dots{} @kindex enable breakpoints -@item enable @var{bnums}@dots{} @kindex enable Enable the specified breakpoints. They become effective once again in stopping the program, until you specify otherwise. @item enable breakpoints once @var{bnums}@dots{} -@item enable once @var{bnums}@dots{} +@itemx enable once @var{bnums}@dots{} Enable the specified breakpoints temporarily. Each will be disabled again the next time it stops the program (unless you have used one of these commands to specify a different state before that time comes). @item enable breakpoints delete @var{bnums}@dots{} -@item enable delete @var{bnums}@dots{} +@itemx enable delete @var{bnums}@dots{} Enable the specified breakpoints to work once and then die. Each of the breakpoints will be deleted the next time it stops the program (unless you have used one of these commands to specify a different @@ -1094,14 +1254,15 @@ is used. @node Conditions, Break Commands, Disabling, Breakpoints @subsection Break Conditions +@cindex conditional breakpoints +@cindex breakpoint conditions -@cindex conditions The simplest sort of breakpoint breaks every time the program reaches a -specified place. You can also specify a @dfn{condition} for a breakpoint. -A condition is just a boolean expression in your programming language -(@xref{Expressions}). A breakpoint with a condition evaluates the -expression each time the program reaches it, and the program stops -only if the condition is true. +specified place. You can also specify a @dfn{condition} for a +breakpoint. A condition is just a boolean expression in your +programming language. (@xref{Expressions}). A breakpoint with a +condition evaluates the expression each time the program reaches it, and +the program stops only if the condition is true. Break conditions may have side effects, and may even call functions in your program. These may sound like strange things to do, but their effects are @@ -1131,12 +1292,16 @@ an ordinary unconditional breakpoint. @end table @cindex ignore count (of breakpoint) -A special feature is provided for one kind of condition: to prevent the -breakpoint from doing anything until it has been reached a certain number -of times. This is done with the @dfn{ignore count} of the breakpoint. -When the program reaches a breakpoint whose ignore count is positive, then -instead of stopping, it just decrements the ignore count by one and -continues. +A special case of a breakpoint condition is to stop only when the +breakpoint has been reached a certain number of times. This is so +useful that there is a special way to do it, using the @dfn{ignore +count} of the breakpoint. Every breakpoint has an ignore count, which +is an integer. Most of the time, the ignore count is zero, and +therefore has no effect. But if the program reaches a breakpoint whose +ignore count is positive, then instead of stopping, it just decrements +the ignore count by one and continues. As a result, if the ignore count +value is @var{n}, the breakpoint will not stop the next @var{n} times it +is reached. @table @code @item ignore @var{bnum} @var{count} @@ -1150,9 +1315,8 @@ a count of zero. @item cont @var{count} Continue execution of the program, setting the ignore count of the breakpoint that the program stopped at to @var{count} minus one. -Continuing through the breakpoint does not itself count as one of -@var{count}. Thus, the program will not stop at this breakpoint until the -@var{count}'th time it is hit. +Thus, the program will not stop at this breakpoint until the +@var{count}'th time it is reached. This command is allowed only when the program stopped due to a breakpoint. At other times, the argument to @samp{cont} is ignored. @@ -1162,10 +1326,9 @@ If a breakpoint has a positive ignore count and a condition, the condition is not checked. Once the ignore count reaches zero, the condition will start to be checked. -Note that you could achieve the effect of the ignore count with a condition -such as @samp{$foo-- <= 0} using a debugger convenience variable that is -decremented each time. That is why the ignore count is considered a -special case of a condition. @xref{Convenience Vars}. +Note that you could achieve the effect of the ignore count with a +condition such as @w{@samp{$foo-- <= 0}} using a debugger convenience +variable that is decremented each time. @xref{Convenience Vars}. @node Break Commands, Error in Breakpoints, Conditions, Breakpoints @subsection Commands Executed on Breaking @@ -1191,8 +1354,8 @@ With no arguments, @samp{commands} refers to the last breakpoint set. It is possible for breakpoint commands to start the program up again. Simply use the @samp{cont} command, or @samp{step}, or any other command to resume execution. However, any remaining breakpoint commands are -ignored. When the program stops again, GDB will act according to why -that stop took place. +ignored. When the program stops again, GDB will act according to the +cause of that stop. @kindex silent If the first command specified is @samp{silent}, the usual message about @@ -1206,13 +1369,11 @@ The commands @samp{echo} and @samp{output} that allow you to print precisely controlled output are often useful in silent breakpoints. @xref{Output}. For example, here is how you could use breakpoint commands to print the -value of @code{x} at entry to @code{foo} whenever it is positive. We -assume that the newly created breakpoint is number 4; @samp{break} will -print the number that is assigned. +value of @code{x} at entry to @code{foo} whenever it is positive. @example break foo if x>0 -commands 4 +commands silent echo x is\040 output x @@ -1231,7 +1392,7 @@ produced. Here is an example: @example break 403 -commands 5 +commands silent set x = y + 4 cont @@ -1256,19 +1417,20 @@ condition 5 (x = y + 4), 0 @end example @noindent -is a condition expression (@xref{Expressions}) that will change @code{x} -as needed, then always have the value 0 so the program will not stop. -Loss of input is avoided here because break conditions are evaluated -without changing the terminal modes. When you want to have nontrivial -conditions for performing the side effects, the operators @samp{&&}, -@samp{||} and @samp{?@: @dots{} :@:} may be useful. +specifies a condition expression (@xref{Expressions}) that will change +@code{x} as needed, then always have the value 0 so the program will not +stop. Loss of input is avoided here because break conditions are +evaluated without changing the terminal modes. When you want to have +nontrivial conditions for performing the side effects, the operators +@samp{&&}, @samp{||} and @samp{?@dots{}:} may be useful. @node Error in Breakpoints,, Break Commands, Breakpoints @subsection ``Cannot Insert Breakpoints'' Error -Under some Unix systems, breakpoints cannot be used in a program if any -other process is running that program. Attempting to run or continue -the program with a breakpoint in this case will cause GDB to stop it. +Under some operating systems, breakpoints cannot be used in a program if +any other process is running that program. Attempting to run or +continue the program with a breakpoint in this case will cause GDB to +stop it. When this happens, you have three ways to proceed: @@ -1282,8 +1444,9 @@ Resume GDB and use the @samp{exec-file} command to specify that GDB should run the program under that name. Then start the program again. @item -Recompile the program so that the text is non-sharable (a.out format -OMAGIC). +Relink the program so that the text segment is nonsharable, using the +linker option @samp{-N}. The operating system limitation may not apply +to nonsharable executables. @end enumerate @node Continuing, Stepping, Breakpoints, Stopping @@ -1302,7 +1465,7 @@ If the program stopped at a breakpoint, the place to continue running is the address of the breakpoint. You might expect that continuing would just stop at the same breakpoint immediately. In fact, @samp{cont} takes special care to prevent that from happening. You do not need -to clear the breakpoint to proceed through it after stopping at it. +to delete the breakpoint to proceed through it after stopping at it. You can, however, specify an ignore-count for the breakpoint that the program stopped at, by means of an argument to the @samp{cont} command. @@ -1332,18 +1495,19 @@ stepping command specifies. @table @code @item step @kindex step -Proceed the program until control reaches a different line, then stop -it and return to the debugger. This command is abbreviated @samp{s}. +Continue running the program until control reaches a different line, +then stop it and return control to the debugger. This command is +abbreviated @samp{s}. -@item step @var{count} -Proceed as in @samp{step}, but do so @var{count} times. If a breakpoint -or a signal not related to stepping is reached before @var{count} steps, -stepping stops right away. - -This command may be given when control is within a routine for which +This command may be given when control is within a function for which there is no debugging information. In that case, execution will proceed -until control reaches a different routine, or is about to return from -this routine. An argument repeats this action. +until control reaches a different function, or is about to return from +this function. An argument repeats this action. + +@item step @var{count} +Continue running as in @samp{step}, but do so @var{count} times. If a +breakpoint is reached or a signal not related to stepping occurs before +@var{count} steps, stepping stops right away. @item next @kindex next @@ -1354,37 +1518,58 @@ different line of code at the stack level which was executing when the An argument is a repeat count, as in @samp{step}. -@samp{next} within a routine without debugging information acts as does +@samp{next} within a function without debugging information acts as does @samp{step}, but any function calls appearing within the code of the -routine are executed without stopping. +function are executed without stopping. @item finish @kindex finish -Continue running until just after the selected stack frame returns -(or until there is some other reason to stop, such as a fatal signal -or a breakpoint). Print value returned by the selected stack frame (if -any). +Continue running until just after the selected stack frame returns (or +until there is some other reason to stop, such as a fatal signal or a +breakpoint). Print value returned by the selected stack frame (if any). Contrast this with the @samp{return} command (@pxref{Returning}). @item until @kindex until -Proceed the program until control reaches a line greater than the current -line, then stop is and return to the debugger. Control is also returned to -the debugger if the program exits the current stack frame. Note that this -form of the command uses single stepping, and hence is slower than -@samp{until} with an argument. This command is abbreviated @samp{u}. +This command is used to avoid single stepping through a loop more than +once. It is like the @samp{next} command, except that when @samp{until} +encounters a jump, it automatically continues execution until the +program counter is greater than the address of the jump. + +This means that when you reach the end of a loop after single stepping +though it, @samp{until} will cause the program to continue execution +until the loop is exited. In contrast, a @samp{next} command at the end +of a loop will simply step back to the beginning of the loop, which +would force you to step through the next iteration. + +@samp{until} always stops the program if it attempts to exit the current +stack frame. + +@samp{until} may produce somewhat counterintuitive results if the order +of the source lines does not match the actual order of execution. For +example, in a typical C @code{for}-loop, the third expression in the +@code{for}-statement (the loop-step expression) is executed after the +statements in the body of the loop, but is written before them. +Therefore, the @samp{until} command would appear to step back to the +beginning of the loop when it advances to this expression. However, it +has not really done so, not in terms of the actual machine code. + +Note that @samp{until} with no argument works by means of single +instruction stepping, and hence is slower than @samp{until} with an +argument. @item until @var{location} -Proceed the program until either the specified location is reached, or the -current (innermost) stack frame returns. This form of the command uses -breakpoints, and hence is quicker than @samp{until} without an argument. +Continue running the program until either the specified location is +reached, or the current (innermost) stack frame returns. This form of +the command uses breakpoints, and hence is quicker than @samp{until} +without an argument. @item stepi @itemx si @kindex stepi @kindex si -Proceed one machine instruction, then stop and return to the debugger. +Execute one machine instruction, then stop and return to the debugger. It is often useful to do @samp{display/i $pc} when stepping by machine instructions. This will cause the next instruction to be executed to @@ -1396,7 +1581,7 @@ An argument is a repeat count, as in @samp{step}. @itemx ni @kindex nexti @kindex ni -Proceed one machine instruction, but if it is a subroutine call, +Execute one machine instruction, but if it is a subroutine call, proceed until the subroutine returns. An argument is a repeat count, as in @samp{next}. @@ -1449,10 +1634,12 @@ frame and describes it briefly as the @samp{frame} command does @section Stack Frames @cindex frame -The call stack is divided up into contiguous pieces called @dfn{frames}; -each frame is the data associated with one call to one function. The frame -contains the arguments given to the function, the function's local -variables, and the address at which the function is executing. +@cindex stack frame +The call stack is divided up into contiguous pieces called @dfn{stack +frames}, or @dfn{frames} for short; each frame is the data associated +with one call to one function. The frame contains the arguments given +to the function, the function's local variables, and the address at +which the function is executing. @cindex initial frame @cindex outermost frame @@ -1487,6 +1674,16 @@ frame using one set of GDB commands, and then other commands will operate on that frame. When your program stops, GDB automatically selects the innermost frame. +@cindex frameless execution +Some functions can be compiled to run without a frame reserved for them +on the stack. This is occasionally done with heavily used library +functions to save the frame setup time. GDB has limited facilities for +dealing with these function invocations; if the innermost function +invocation has no stack frame, GDB will give it a virtual stack frame of +0 and correctly allow tracing of the function call chain. Results are +undefined if a function invocation besides the innermost one is +frameless. + @node Backtrace, Selection, Frames, Stack @section Backtraces @@ -1498,6 +1695,8 @@ stack. @table @code @item backtrace @itemx bt +@kindex backtrace +@kindex bt Print a backtrace of the entire stack: one line per frame for all frames in the stack. @@ -1506,19 +1705,47 @@ character, normally @kbd{Control-C}. @item backtrace @var{n} @itemx bt @var{n} -Similar, but stop after @var{n} frames. +Similar, but print only the innermost @var{n} frames. @item backtrace @var{-n} @itemx bt @var{-n} -Similar, but print the outermost @var{n} frames instead of the -innermost. +Similar, but print only the outermost @var{n} frames. @end table -Each line in a backtrace shows the frame number, the program counter, the -function and its arguments, and the source file name and line number (if -known). The program counter is omitted if is the beginning of the code for -the source line. This is the same as the first of the two lines printed -when you select a frame. +@kindex where +@kindex info stack +The names @samp{where} and @samp{info stack} are additional aliases +for @samp{backtrace}. + +Every line in the backtrace shows the frame number, the function name +and the program counter value. + +If the function is in a source file whose symbol table data has been +fully read, the backtrace shows the source file name and line number, as +well as the arguments to the function. (The program counter value is +omitted if it is at the beginning of the code for that line number.) + +If the source file's symbol data has not been fully read, just scanned, +this extra information is replaced with an ellipsis. You can force the +symbol data for that frame's source file to be read by selecting the +frame. (@xref{Selection}). + +Here is an example of a backtrace. It was made with the command +@samp{bt 3}, so it shows the innermost three frames. + +@example +#0 rtx_equal_p (x=(rtx) 0x8e58c, y=(rtx) 0x1086c4) (/gp/rms/cc/rtlanal.c line 337) +#1 0x246b0 in expand_call (...) (...) +#2 0x21cfc in expand_expr (...) (...) +(More stack frames follow...) +@end example + +@noindent +The functions @code{expand_call} and @code{expand_expr} are in a file +whose symbol details have not been fully read. Full detail is available +for the function @code{rtx_equal_p}, which is in the file +@file{rtlanal.c}. Its arguments, named @code{x} and @code{y}, are shown +with their typed values. @node Selection, Frame Info, Backtrace, Stack @section Selecting a Frame @@ -1653,7 +1880,7 @@ printed; however, if the last line printed was a solitary line printed as part of displaying a stack frame (@pxref{Stack}), this prints ten lines centered around that line. -@item list @minus{} +@item list - Print ten lines just before the lines last printed. @end table @@ -1663,6 +1890,7 @@ than listing the same lines again. An exception is made for an argument of @samp{-}; that argument is preserved in repetition so that each repetition moves up in the file. +@cindex linespec In general, the @samp{list} command expects you to supply zero, one or two @dfn{linespecs}. Linespecs specify source lines; there are several ways of writing them but the effect is always to specify some source line. @@ -1685,7 +1913,7 @@ Print ten lines starting with @var{first}. @item list + Print ten lines just after the lines last printed. -@item list @minus{} +@item list - Print ten lines just before the lines last printed. @item list @@ -1695,7 +1923,7 @@ As described in the preceding table. Here are the ways of specifying a single source line---all the kinds of linespec. -@table @asis +@table @code @item @var{linenum} Specifies line @var{linenum} of the current source file. When a @samp{list} command has two linespecs, this refers to @@ -1707,7 +1935,7 @@ When used as the second linespec in a @samp{list} command that has two, this specifies the line @var{offset} lines down from the first linespec. -@item @minus{}@var{offset} +@item -@var{offset} Specifies the line @var{offset} lines before the last line printed. @item @var{filename}:@var{linenum} @@ -1740,7 +1968,7 @@ source line @var{linenum}. The default examine address for the @samp{x} command is changed to the starting address of the line, so that @samp{x/i} is sufficient to begin examining the machine code (@pxref{Memory}). Also, this address -is saved as the value of the convenience variable @samp{$_} +is saved as the value of the convenience variable @code{$_} (@pxref{Convenience Vars}). @end table @@ -1768,31 +1996,33 @@ this command with as little as @samp{rev}. @cindex source path @cindex directories for source files -Executable programs do not record the directories of the source files they -were compiled from, just the names. GDB remembers a list of directories to -search for source files; this is called the @dfn{source path}. Each time -GDB wants a source file, it tries all the directories in the list, in the -order they are present in the list, until it finds a file with the desired -name. +Executable programs do not record the directories of the source files +from which they were compiled, just the names. GDB remembers a list of +directories to search for source files; this is called the @dfn{source +path}. Each time GDB wants a source file, it tries all the directories +in the list, in the order they are present in the list, until it finds a +file with the desired name. @b{Note that the executable search path is +@i{not} used for this purpose. Neither is the current working +directory, unless it happens to be in the source path.} @kindex directory When you start GDB, its source path contains just the current working directory. To add other directories, use the @samp{directory} command. -@b{Note that the search path for executable files and the working directory -are @i{not} used for finding source files.} @table @code -@item directory @var{dirname} -Add directory @var{dirname} to the end of the source path. +@item directory @var{dirnames...} +Add directory @var{dirname} to the end of the source path. Several +directory names may be given to this command, separated by whitespace or +@samp{:}. @item directory Reset the source path to just the current working directory of GDB. This requires confirmation. -@samp{directory} with no argument can cause source files previously -found by GDB to be found in a different directory. To make this work -correctly, this command also clears out the tables GDB maintains -about the source files it has already found. +Since this command deletes directories from the search path, it may +change the directory in which a previously read source file will be +discovered. To make this work correctly, this command also clears out +the tables GDB maintains about the source files it has already found. @item info directories @kindex info directories @@ -1825,7 +2055,7 @@ directories you want in the source path. @cindex printing data @cindex examining data @kindex print -The usual way of examining data in your program is with the @samp{print} +The usual way to examine data in your program is with the @samp{print} command (abbreviated @samp{p}). It evaluates and prints the value of any valid expression of the language the program is written in (for now, C). You type @@ -1842,21 +2072,13 @@ A more low-level way of examining data is with the @samp{x} command. It examines data in memory at a specified address and prints it in a specified format. -GDB supports one command to modify the default format of displayed data: - -@table @samp -@item set array-max -@kindex set array-max -@samp{set array-max} sets the maximum number of elements of an array which -will be printed. This limit also applies to the display of strings. -@end table - @menu * Expressions:: Expressions that can be computed and printed. * Variables:: Using your program's variables in expressions. * Assignment:: Setting your program's variables. * Arrays:: Examining part of memory as an array. -* Formats:: Specifying formats for printing values. +* Format Options:: Controlling how structures and arrays are printed. +* Output formats:: Specifying formats for printing values. * Memory:: Examining memory explicitly. * Auto Display:: Printing certain expressions whenever program stops. * Value History:: Referring to values previously printed. @@ -1873,7 +2095,7 @@ Any kind of constant, variable or operator defined by the programming language you are using is legal in an expression in GDB. This includes conditional expressions, function calls, casts and string constants. It unfortunately does not include symbols defined by preprocessor -#define commands. +@code{#define} commands. Casts are supported in all languages, not just in C, because it is so useful to cast a number into a pointer so as to examine a structure @@ -1942,7 +2164,7 @@ you can specify any one of them using the colon-colon construct: @noindent Here @var{block} is the name of the source file whose variable you want. -@node Arrays, Formats, Variables, Data +@node Arrays, Format options, Variables, Data @section Artificial Arrays @cindex artificial array @@ -1977,8 +2199,91 @@ subscripting, and are coerced to pointers when used in expressions. (It would probably appear in an expression via the value history, after you had printed it out.) -@node Formats, Memory, Arrays, Data -@section Formats +@node Format options, Output formats, Arrays, Data +@section Format options + +@cindex format options +GDB provides a few ways to control how arrays and structures are +printed. + +@table @code +@item info format +@kindex info format +Display the current settings for the format options. + +@item set array-max @var{number-of-elements} +@kindex set array-max +If GDB is printing a large array, it will stop printing after it has +printed the number of elements set by the @samp{set array-max} command. +This limit also applies to the display of strings. + +@item set prettyprint on +@kindex set prettyprint +Cause GDB to print structures in an indented format with one member per +line, like this: + +@example +$1 = @{ + next = 0x0, + flags = @{ + sweet = 1, + sour = 1 + @}, + meat = 0x54 "Pork" +@} +@end example + +@item set prettyprint off +Cause GDB to print structures in a compact format, like this: + +@example +$1 = @{next = 0x0, flags = @{sweet = 1, sour = 1@}, meat = 0x54 "Pork"@} +@end example + +This is the default format. + +@item set unionprint on +@kindex set unionprint +Tell GDB to print unions which are contained in structures. This is the +default setting. +@item set unionprint off +Tell GDB not to print unions which are contained in structures. + +For example, given the declarations + +@example +typedef enum @{Tree, Bug@} Species; +typedef enum @{Big_tree, Acorn, Seedling@} Tree_forms; +typedef enum @{Caterpiller, Cocoon, Butterfly@} Bug_forms; + +struct thing @{ + Species it; + union @{ + Tree_forms tree; + Bug_forms bug; + @} form; +@}; + +struct thing foo = @{Tree, @{Acorn@}@}; +@end example + +@noindent +with @samp{set unionprint on} in effect @samp{p foo} would print + +@example +$1 = @{it = Tree, form = @{tree = Acorn, bug = Cocoon@}@} +@end example + +@noindent +and with @samp{set unionprint off} in effect it would print + +@example +$1 = @{it = Tree, form = @{...@}@} +@end example +@end table + +@node Output formats, Memory, Format options, Data +@section Output formats @cindex formatted output @cindex output formats @@ -2033,19 +2338,22 @@ To reprint the last value in the value history with a different format, you can use the @samp{print} command with just a format and no expression. For example, @samp{p/x} reprints the last value in hex. -@node Memory, Auto Display, Formats, Data +@node Memory, Auto Display, Output formats, Data @subsection Examining Memory @cindex examining memory @kindex x -The command @samp{x} (for `examine') can be used to examine memory under -explicit control of formats, without reference to the program's data types. +The command @samp{x} (for `examine') can be used to examine memory +without reference to the program's data types. The format in which you +wish to examine memory is instead explicitly specified. The allowable +formats are a superset of the formats described in the previous section. @samp{x} is followed by a slash and an output format specification, followed by an expression for an address. The expression need not have a pointer value (though it may); it is used as an integer, as the -address of a byte of memory. @xref{Expressions} for more information -on expressions. +address of a byte of memory. @xref{Expressions} for more information on +expressions. For example, @samp{x/4xw $sp} prints the four words of +memory above the stack pointer in hexadecimal. The output format in this case specifies both how big a unit of memory to examine and how to print the contents of that unit. It is done @@ -2068,7 +2376,7 @@ Many assemblers and cpu designers still use `word' for a 16-bit quantity, as a holdover from specific predecessor machines of the 1970's that really did use two-byte words. But more generally the term `word' has always referred to the size of quantity that a machine normally operates on and -stores in its registers. This is 32 bits for all the machines that GNU +stores in its registers. This is 32 bits for all the machines that GDB runs on. @item g @@ -2137,14 +2445,14 @@ You can examine several consecutive units of memory with one command by writing a repeat-count after the slash (before the format letters, if any). The repeat count must be a decimal integer. It has the same effect as repeating the @samp{x} command that many times except that the output may -be more compact with several units per line. +be more compact with several units per line. For example, @example x/10i $pc @end example @noindent -Prints ten instructions starting with the one to be executed next in the +prints ten instructions starting with the one to be executed next in the selected frame. After doing this, you could print another ten following instructions with @@ -2160,19 +2468,29 @@ in which the format and address are allowed to default. The addresses and contents printed by the @samp{x} command are not put in the value history because there is often too much of them and they would get in the way. Instead, GDB makes these values available for subsequent -use in expressions as values of the convenience variables @samp{$_} and -@samp{$__}. +use in expressions as values of the convenience variables @code{$_} and +@code{$__}. After an @samp{x} command, the last address examined is available for use -in expressions in the convenience variable @samp{$_}. The contents of that -address, as examined, are available in the convenience variable @samp{$__}. +in expressions in the convenience variable @code{$_}. The contents of that +address, as examined, are available in the convenience variable @code{$__}. If the @samp{x} command has a repeat count, the address and contents saved are from the last memory unit printed; this is not the same as the last address printed if several units were printed on the last line of output. +@kindex disassemble +The specialized command @samp{disassemble} is also provided to dump a +range of memory as machine instructions. The default memory range is +the function surrounding the program counter of the selected frame. A +single argument to this command is a program counter value; the function +surrounding this value will be dumped. Two arguments specify a range of +addresss (first inclusive, second exclusive) to be dumped. + @node Auto Display, Value History, Memory, Data @section Automatic Display +@cindex automatic display +@cindex display of expressions If you find that you want to print the value of an expression frequently (to see how it changes), you might want to add it to the @dfn{automatic @@ -2189,6 +2507,14 @@ The automatic display looks like this: @noindent showing item numbers, expressions and their current values. +If the expression refers to local variables, then it does not make sense +outside the lexical context for which it was set up. Such an expression +is printed only when execution is inside that lexical context. For +example, if you give the command @samp{display name} while inside a +function with an argument @code{name}, then this argument will be +displayed whenever the program stops inside that function, but not when +it stops elsewhere (since this argument doesn't exist elsewhere). + @table @code @item display @var{exp} @kindex display @@ -2207,15 +2533,16 @@ be examined each time the program stops. Examining means in effect doing @samp{x/@var{fmt} @var{addr}}. @xref{Memory}. @item undisplay @var{dnums}@dots{} -@kindex undisplay -@item delete display @var{dnums}@dots{} +@itemx delete display @var{dnums}@dots{} @kindex delete display +@kindex undisplay Remove item numbers @var{dnums} from the list of expressions to display. @item disable display @var{dnums}@dots{} @kindex disable display -Disable the display of item numbers @var{dnums}. A disabled display item -has no effect but is not forgotten. It may be later enabled. +Disable the display of item numbers @var{dnums}. A disabled display +item is not printed automatically, but is not forgotten. It may be +reenabled later. @item enable display @var{dnums}@dots{} @kindex enable display @@ -2228,8 +2555,11 @@ done when the program stops. @item info display @kindex info display -Print the list of expressions to display automatically, each one -with its item number, but without showing the values. +Print the list of expressions previously set up to display +automatically, each one with its item number, but without showing the +values. This includes disabled expressions, which are marked as such. +It also includes expressions which would not be displayed right now +because they refer to automatic variables not currently available. @end table @node Value History, Convenience Vars, Auto Display, Data @@ -2240,17 +2570,18 @@ Every value printed by the @samp{print} command is saved for the entire session in GDB's @dfn{value history} so that you can refer to it in other expressions. -@cindex $ -@cindex $$ +@cindex @code{$} +@cindex @code{$$} +@cindex history number The values printed are given @dfn{history numbers} for you to refer to them by. These are successive integers starting with 1. @samp{print} shows you -the history number assigned to a value by printing @samp{$@var{n} = } -before the value; here @var{n} is the history number. +the history number assigned to a value by printing @samp{$@var{num} = } +before the value; here @var{num} is the history number. To refer to any previous value, use @samp{$} followed by the value's history number. The output printed by @samp{print} is designed to remind -you of this. Just @samp{$} refers to the most recent value in the history, -and @samp{$$} refers to the value before that. +you of this. Just @code{$} refers to the most recent value in the history, +and @code{$$} refers to the value before that. For example, suppose you have just printed a pointer to a structure and want to see the contents of the structure. It suffices to type @@ -2260,16 +2591,17 @@ p *$ @end example If you have a chain of structures where the component @samp{next} points -to the next one, you can print the contents of the next one with +to the next one, you can print the contents of the next one with this: @example p *$.next @end example +@noindent It might be useful to repeat this command many times by typing @key{RET}. Note that the history records values, not expressions. If the value of -@code{x} is 4 and you type +@code{x} is 4 and you type this command: @example print x @@ -2278,17 +2610,20 @@ set x=5 @noindent then the value recorded in the value history by the @samp{print} command -remains 4 even though @code{x}'s value has changed. +remains 4 even though the value of @code{x} has changed. @table @code -@item info history -@kindex info history +@item info values +@kindex info values Print the last ten values in the value history, with their item numbers. This is like @samp{p $$9} repeated ten times, except that -@samp{info history} does not change the history. +@samp{info values} does not change the history. -@item info history @var{n} +@item info values @var{n} Print ten history values centered on history item number @var{n}. + +@item info values + +Print ten history values just after the values last printed. @end table @node Convenience Vars, Registers, Value History, Data @@ -2313,7 +2648,7 @@ set $foo = *object_ptr @end example @noindent -would save in @samp{$foo} the value contained in the object pointed to by +would save in @code{$foo} the value contained in the object pointed to by @code{object_ptr}. Using a convenience variable for the first time creates it; but its value @@ -2344,16 +2679,16 @@ print bar[$i++]->contents Some convenience variables are created automatically by GDB and given values likely to be useful. -@table @samp +@table @code @item $_ -The variable @samp{$_} is automatically set by the @samp{x} command to +The variable @code{$_} is automatically set by the @samp{x} command to the last address examined (@pxref{Memory}). Other commands which -provide a default address for @samp{x} to examine also set @samp{$_} +provide a default address for @samp{x} to examine also set @code{$_} to that address; these commands include @samp{info line} and @samp{info breakpoint}. @item $__ -The variable @samp{$__} is automatically set by the @samp{x} command +The variable @code{$__} is automatically set by the @samp{x} command to the value found in the last address examined. @end table @@ -2364,9 +2699,15 @@ to the value found in the last address examined. Machine register contents can be referred to in expressions as variables with names starting with @samp{$}. The names of registers are different for each machine; use @samp{info registers} to see the names used on your -machine. The names @samp{$pc} and @samp{$sp} are used on all machines for -the program counter register and the stack pointer. Often @samp{$fp} is -used for a register that contains a pointer to the current stack frame. +machine. The names @code{$pc} and @code{$sp} are used on all machines for +the program counter register and the stack pointer. Often @code{$fp} is +used for a register that contains a pointer to the current stack frame, +and @code{$ps} is used for a register that contains the processor +status. These standard register names may be available on your machine +even though the @code{info registers} command displays them with a +different name. For example, on the SPARC, @code{info registers} +displays the processor status register as @code{$psr} but you can also +refer to it as @code{$ps}. GDB always considers the contents of an ordinary register as an integer when the register is examined in this way. Some machines have special @@ -2379,7 +2720,7 @@ Some registers have distinct ``raw'' and ``virtual'' data formats. This means that the data format in which the register contents are saved by the operating system is not the same one that your program normally sees. For example, the registers of the 68881 floating point coprocessor are always -saved in ``extended'' format, but virtually all C programs expect to work with +saved in ``extended'' format, but all C programs expect to work with ``double'' format. In such cases, GDB normally works with the virtual format only (the format that makes sense for your program), but the @samp{info registers} command prints the data in both formats. @@ -2430,7 +2771,7 @@ set $sp += 4 @noindent The last is a way of removing one word from the stack, on machines where stacks grow downward in memory (most machines, nowadays). This assumes -that the innermost stack frame is selected. Setting @samp{$sp} is +that the innermost stack frame is selected. Setting @code{$sp} is not allowed when other stack frames are selected. @node Symbols, Altering, Data, Top @@ -2451,16 +2792,18 @@ assignments or function calls) inside it do not take place. @xref{Expressions}. @item whatis -Print the data type of @samp{$}, the last value in the value history. +Print the data type of @code{$}, the last value in the value history. @item info address @var{symbol} @kindex info address -Describe where the data for @var{symbol} is stored. For register -variables, this says which register. For other automatic variables, -this prints the stack-frame offset at which the variable is always -stored. Note the contrast with @samp{print &@var{symbol}}, which does -not work at all for register variables and for automatic variables -prints the exact address of the current instantiation of the variable. +Describe where the data for @var{symbol} is stored. For a register +variable, this says which register it is kept in. For a non-register +local variable, this prints the stack-frame offset at which the variable +is always stored. + +Note the contrast with @samp{print &@var{symbol}}, which does not work +at all for a register variables, and for a stack local variable prints +the exact address of the current instantiation of the variable. @item ptype @var{typename} @kindex ptype @@ -2488,11 +2831,11 @@ start with @samp{step}. @item info variables @kindex info variables Print the names and data types of all variables that are declared -outside of functions. +outside of functions (i.e., except for local variables). @item info variables @var{regexp} -Print the names and data types of all variables, declared outside of -functions, whose names contain a match for regular expression +Print the names and data types of all variables (except for local +variables) whose names contain a match for regular expression @var{regexp}. @item info types @@ -2504,17 +2847,15 @@ Print all data types that are defined in the program whose names contain a match for regular expression @var{regexp}. @item info methods -@item info methods @var{regexp} +@itemx info methods @var{regexp} @kindex info methods The @samp{info-methods} command permits the user to examine all defined -methods within C@code{++} program, or (with the @var{regexp} argument) a -specific set of methods found in the various C@code{++} classes. Many -C@code{++} classes which implement a large number of differently typed -methods implement a large number of methods as well. Thus, the -@samp{ptype} command can give the user a tremendous overdose of -information about what methods are associated with a given class. The -@samp{info-methods} command filters these methods do to only those -methods which match the regular-expression search key. +methods within C++ program, or (with the @var{regexp} argument) a +specific set of methods found in the various C++ classes. Many +C++ classes provide a large number of methods. Thus, the output +from the @samp{ptype} command can be overwhelming and hard to use. The +@samp{info-methods} command filters the methods, printing only those +which match the regular-expression @var{regexp}. @item printsyms @var{filename} @kindex printsyms @@ -2525,8 +2866,15 @@ file @var{filename}. @node Altering, Sequences, Symbols, Top @chapter Altering Execution -There are several ways to alter the execution of your program with GDB -commands. +Once you think you have find an error in the program, you might want to +find out for certain whether correcting the apparent error would lead to +correct results in the rest of the run. You can find the answer by +experiment, using the GDB features for altering execution of the +program. + +For example, you can store new values into variables or memory +locations, give the program a signal, restart it at a different address, +or even return prematurely from a function to its caller. @menu * Assignment:: Altering variable values or memory contents. @@ -2551,6 +2899,10 @@ print x=4 would store the value 4 into the variable @code{x}, and then print the value of the assignment expression (which is 4). +All the assignment operators of C are supported, including the +incrementation operators @samp{++} and @samp{--}, and combining +assignments such as @samp{+=} and @samp{<<=}. + @kindex set @kindex set variable If you are not interested in seeing the value of the assignment, use the @@ -2569,20 +2921,25 @@ freely store an integer value into a pointer variable or vice versa, and any structure can be converted to any other structure that is the same length or shorter. -In C, all the other assignment operators such as @samp{+=} and @samp{++} -are supported as well. - -To store into arbitrary places in memory, use the @samp{@{@dots{}@}} +To store values into arbitrary places in memory, use the @samp{@{@dots{}@}} construct to generate a value of specified type at a specified address -(@pxref{Expressions}). For example, +(@pxref{Expressions}). For example, @code{@{int@}0x83040} would refer +to memory location 0x83040 as an integer (which implies a certain size +and representation in memory), and @example set @{int@}0x83040 = 4 @end example +would store the value 4 into that memory location. + @node Jumping, Signaling, Assignment, Altering @section Continuing at a Different Address +Ordinarily, when you continue the program, you do so at the place where +it stopped, with the @samp{cont} command. You can instead continue at +an address of your own choosing, with the following commands: + @table @code @item jump @var{linenum} @kindex jump @@ -2593,27 +2950,43 @@ The @samp{jump} command does not change the current stack frame, or the stack pointer, or the contents of any memory location or any register other than the program counter. If line @var{linenum} is in a different function from the one currently executing, the results may -be wild if the two functions expect different patterns of arguments or +be bizarre if the two functions expect different patterns of arguments or of local variables. For this reason, the @samp{jump} command requests confirmation if the specified line is not in the function currently -executing. However, even wild results are predictable based on -changing the program counter. +executing. However, even bizarre results are predictable based on +careful study of the machine-language code of the program. @item jump *@var{address} Resume execution at the instruction at address @var{address}. @end table -A similar effect can be obtained by storing a new value into the register -@samp{$pc}, but not exactly the same. +You can get much the same effect as the @code{jump} command by storing a +new value into the register @code{$pc}. The difference is that this +does not start the program running; it only changes the address where it +@emph{will} run when it is continued. For example, @example set $pc = 0x485 @end example @noindent -specifies the address at which execution will resume, but does not resume -execution. That does not happen until you use the @samp{cont} command or a -stepping command (@pxref{Stepping}). +causes the next @samp{cont} command or stepping command to execute at +address 0x485, rather than at the address where the program stopped. +@xref{Stepping}. + +The most common occasion to use the @samp{jump} command is when you have +stepped across a function call with @code{next}, and found that the +return value is incorrect. If all the relevant data appeared correct +before the function call, the error is probably in the function that +just returned. + +In general, your next step would now be to rerun the program and execute +up to this function call, and then step into it to see where it goes +astray. But this may be time consuming. If the function did not have +significant side effects, you could get the same information by resuming +execution just before the function call and stepping through it. To do this, +first put a breakpoint on that function; then, use the @samp{jump} command +to continue on the line with the function call. @node Signaling, Returning, Jumping, Altering @section Giving the Program a Signal @@ -2621,13 +2994,14 @@ stepping command (@pxref{Stepping}). @table @code @item signal @var{signalnum} @kindex signal -Resume execution where the program stopped, but give it immediately -the signal number @var{signalnum}. - -Alternatively, if @var{signalnum} is zero, continue execution and give -no signal. This is useful when the program has received a signal -but you don't want the program to see that signal; the @samp{cont} command -would signal the program. +Resume execution where the program stopped, but give it immediately the +signal number @var{signalnum}. + +Alternatively, if @var{signalnum} is zero, continue execution without +giving a signal. This is useful when the program stopped on account of +a signal and would ordinary see the signal when resumed with the +@samp{cont} command; @samp{signal 0} causes it to resume without a +signal. @end table @node Returning,, Signaling, Altering @@ -2635,24 +3009,28 @@ would signal the program. @cindex returning from a function @kindex return -You can make any function call return immediately, using the @samp{return} -command. +You can cancel execution of a function call with the @samp{return} +command. This command has the effect of discarding the selected stack +frame (and all frames within it), so that control moves to the caller of +that function. You can think of this as making the discarded frame +return prematurely. First select the stack frame that you wish to return from -(@pxref{Selection}). Then type the @samp{return} command. If you wish to -specify the value to be returned, give that as an argument. +(@pxref{Selection}). Then type the @samp{return} command. If you wish +to specify the value to be returned, give that as an argument. This pops the selected stack frame (and any other frames inside of it), leaving its caller as the innermost remaining frame. That frame becomes selected. The specified value is stored in the registers used for returning values of functions. -The @samp{return} command does not resume execution; it leaves the program -stopped in the state that would exist if the function had just returned. -Contrast this with the @samp{finish} command (@pxref{Stepping}), which -resumes execution @i{until} the selected stack frame returns naturally. +The @samp{return} command does not resume execution; it leaves the +program stopped in the state that would exist if the function had just +returned. Contrast this with the @samp{finish} command +(@pxref{Stepping}), which resumes execution until the selected stack +frame returns @emph{naturally}. -@node Sequences, Emacs, Altering, Top +@node Sequences, Options, Altering, Top @chapter Canned Sequences of Commands GDB provides two ways to store sequences of commands for execution as a @@ -2668,7 +3046,7 @@ unit: user-defined commands and command files. @node Define, Command Files, Sequences, Sequences @section User-Defined Commands -@cindex user-defined commands +@cindex user-defined command A @dfn{user-defined command} is a sequence of GDB commands to which you assign a new name as a command. This is done with the @samp{define} command. @@ -2688,9 +3066,9 @@ commands is marked by a line containing @samp{end}. Give documentation to the user-defined command @var{commandname}. The command @var{commandname} must already be defined. This command reads lines of documentation just as @samp{define} reads the lines of the -command definition, ending with @samp{end}. After the @samp{document} command is finished, -@samp{help} on command @var{commandname} will print the documentation -you have specified. +command definition, ending with @samp{end}. After the @samp{document} +command is finished, @samp{help} on command @var{commandname} will print +the documentation you have specified. You may use the @samp{document} command again to change the documentation of a command. Redefining the command with @samp{define} @@ -2716,7 +3094,7 @@ command file does nothing; it does not mean to repeat the last command, as it would from the terminal. @cindex init file -@cindex .gdbinit +@cindex @file{.gdbinit} When GDB starts, it automatically executes its @dfn{init files}, command files named @file{.gdbinit}. GDB reads the init file (if any) in your home directory and then the init file (if any) in the current working @@ -2750,30 +3128,46 @@ exactly the output you want. @table @code @item echo @var{text} @kindex echo -Print @var{text}. Nonprinting characters can be included in -@var{text} using C escape sequences, such as @samp{\n} to print a -newline. @b{No newline will be printed unless you specify one.} +@comment I don't consider backslash-space a standard C escape sequence +@comment because it's not in ANSI. +Print @var{text}. Nonprinting characters can be included in @var{text} +using C escape sequences, such as @samp{\n} to print a newline. @b{No +newline will be printed unless you specify one.} In addition to the +standard C escape sequences a backslash followed by a space stands for a +space. This is useful for outputting a string with spaces at the +beginning or the end, since leading and trailing spaces are trimmed from +all arguments. Thus, to print @w{`` and foo = ''}, use the command +@w{``echo \ and foo = \ ''}. +@comment AAARGGG! How am I supposed to do @samp{ and foo = } and not +@comment have the spaces be invisible in TeX? + +A backslash at the end of @var{text} can be used, as in C, to continue +the command onto subsequent lines. For example, -A backslash at the end of @var{text} is ignored. It is useful for -outputting a string ending in spaces, since trailing spaces are -trimmed from all arguments. A backslash at the beginning preserves -leading spaces in the same way, because @samp{\ } as an escape -sequence stands for a space. Thus, to print @samp{ and foo = }, do +@example +echo This is some text\n\ +which is continued\n\ +onto several lines.\n +@end example + +produces the same output as @example -echo \ and foo = \ +echo This is some text\n +echo which is continued\n +echo onto several lines.\n @end example @item output @var{expression} @kindex output Print the value of @var{expression} and nothing but that value: no newlines, no @samp{$@var{nn} = }. The value is not entered in the -value history either. @xref{Expressions} for more information -on expressions. +value history either. @xref{Expressions} for more information on +expressions. @item output/@var{fmt} @var{expression} Print the value of @var{expression} in format @var{fmt}. -@xref{Formats}, for more information. +@xref{Output formats}, for more information. @item printf @var{string}, @var{expressions}@dots{} @kindex printf @@ -2796,19 +3190,101 @@ The only backslash-escape sequences that you can use in the string are the simple ones that consist of backslash followed by a letter. @end table -@node Emacs, Remote, Sequences, Top +@node Options, Emacs, Sequences, Top +@chapter Options and Arguments for GDB + +When you invoke GDB, you can specify arguments telling it what files to +operate on and what other things to do. + +@menu +* Mode Options:: Options controlling modes of operation. +* File Options:: Options to specify files (executable, coredump, commands) +* Other Arguments:: Any other arguments without options + also specify files. +@end menu + +@node Mode Options, File Options, Options, Options +@section Mode Options + +@table @samp +@item -nx +Do not execute commands from the init files @file{.gdbinit}. +Normally, the commands in these files are executed after all the +command options and arguments have been processed. @xref{Command +Files}. + +@item -q +``Quiet''. Do not print the usual introductory messages. + +@item -batch +Run in batch mode. Exit with code 0 after processing all the command +files specified with @samp{-x} (and @file{.gdbinit}, if not inhibited). +Exit with nonzero status if an error occurs in executing the GDB +commands in the command files. + +@item -fullname +This option is used when Emacs runs GDB as a subprocess. It tells GDB +to output the full file name and line number in a standard, +recognizable fashion each time a stack frame is displayed (which +includes each time the program stops). This recognizable format looks +like two @samp{\032} characters, followed by the file name, line number +and character position separated by colons, and a newline. The +Emacs-to-GDB interface program uses the two @samp{\032} characters as +a signal to display the source code for the frame. +@end table + +@node File Options, Other Arguments, Mode Options, Options +@section File-specifying Options + +All the options and command line arguments given are processed +in sequential order. The order makes a difference when the +@samp{-x} option is used. + +@table @samp +@item -s @var{file} +Read symbol table from file @var{file}. + +@item -e @var{file} +Use file @var{file} as the executable file to execute when +appropriate, and for examining pure data in conjunction with a core +dump. + +@item -se @var{file} +Read symbol table from file @var{file} and use it as the executable +file. + +@item -c @var{file} +Use file @var{file} as a core dump to examine. + +@item -x @var{file} +Execute GDB commands from file @var{file}. + +@item -d @var{directory} +Add @var{directory} to the path to search for source files. +@end table + +@node Other Arguments,, File Options, Options +@section Other Arguments + +If there are arguments to GDB that are not options or associated with +options, the first one specifies the symbol table and executable file name +(as if it were preceded by @samp{-se}) and the second one specifies a core +dump file name (as if it were preceded by @samp{-c}). + +@node Emacs, Remote, Options, Top @chapter Using GDB under GNU Emacs A special interface allows you to use GNU Emacs to view (and edit) the source files for the program you are debugging with GDB. -To use this interface, use the command @kbd{M-x gdb} in Emacs. -Give the executable file you want to debug as an argument. This -command starts a GDB process as a subprocess of Emacs, with input -and output through a newly created Emacs buffer. +To use this interface, use the command @kbd{M-x gdb} in Emacs. Give the +executable file you want to debug as an argument. This command starts +GDB as a subprocess of Emacs, with input and output through a newly +created Emacs buffer. -Using this GDB process is just like using GDB normally except for two things: +Using GDB under Emacs is just like using GDB normally except for two +things: @itemize @bullet @item @@ -2844,19 +3320,12 @@ calls, like the GDB @samp{next} command. @item M-i Execute one instruction, like the GDB @samp{stepi} command. -@item M-u -Move up one stack frame (and display that frame's source file in -Emacs), like the GDB @samp{up} command. - -@item M-d -Move down one stack frame (and display that frame's source file in -Emacs), like the GDB @samp{down} command. (This means that you cannot -delete words in the usual fashion in the GDB buffer; I am guessing you -won't often want to do that.) - @item C-c C-f Execute until exit from the selected stack frame, like the GDB @samp{finish} command. + +@item C-c C-c +Continue execution of the program, like the GDB @samp{cont} command. @end table In any source file, the Emacs command @kbd{C-x SPC} (@code{gdb-break}) @@ -2910,15 +3379,109 @@ step and continue the remote program. To resume the remote program and stop debugging it, use the @samp{detach} command. +@ignore +This material will be merged in when better Readline documentation +is done. + +@node GDB Readline, History Top ,Readline Top, Command Editing +@subsection GDB Readline + +You may control the behavior of command line editing in GDB with the +following commands: + +@table @code +@kindex set editing +@item set editing +@itemx set editing on +Enable command line editing (enabled by default). + +@item set editing off +Disable command line editing. + +@kindex set history file +@item set history file @var{filename} +Set the name of the GDB command history file to @var{filename}. This is +the file from which GDB will read an initial command history +list or to which it will write this list when it exits. This list is +accessed through history expansion or through the history +command editing characters listed below. This file defaults to the +value of the environmental variable @code{GDBHISTFILE}, or to +@code{./.gdb_history} if this variable is not set. + +@kindex set history write +@item set history write +@itemx set history write on +Enable the writing of the command history to the command history file +named above. This is enabled by default. + +@item set history write off +Disable the writing of the command history to the command history file. + +@kindex set history size +@item set history size @var{size} +Set the number of commands which GDB will keep in its history list. +This defaults to the value of the environmental variable +@code{HISTSIZE}, or to 256 if this variable is not set. + +@kindex info editing +@item info editing +Display the current settings relating to command line editing, and also +display the last ten commands in the command history. + +@item info editing @var{n} +Print ten commands centered on command number @var{n}. + +@item info editing + +Print ten commands just after the commands last printed. +@end table + +@node GDB History, , History Top, Command editing +@comment node-name, next, previous, up +Note that because of the additional meaning of @code{!} to GDB (as the +logical not operator in C), history expansion is off by default. If you +decide to enable history expansion with the @samp{set history expansion +on} command, you will need to follow @samp{!} with a space or a tab to +prevent it from being expanded. + +The commands to control history expansion are: + +@table @code + +@kindex set history expansion +@item set history expansion on +@itemx set history expansion +Enable history expansion. + +@item set history expansion off +Disable history expansion. History expansion is off by default. + +@end table +@end ignore + @node Commands, Concepts, Remote, Top @unnumbered Command Index @printindex ky -@node Concepts,, Commands, Top +@node Concepts, , Commands, Top @unnumbered Concept Index @printindex cp @contents @bye + + + + +Occasionally it is useful to execute a shell command from within GDB. +This can be done with the @samp{shell} command. + +@table @code +@item shell @var{shell command string} +@kindex shell +@cindex shell escape +Directs GDB to invoke an inferior shell to execute @var{shell command string}. +The environment variable @code{SHELL} is used if it exists, otherwise GDB +uses @samp{/bin/sh}. +@end table |